1. Field of the Invention
The present invention relates generally to ultrasonic extrusion apparatuses which cause resonance of extrusion dies using ultrasonic vibrations, thus reducing friction between the extrusion dies and extrusion materials and, more particularly, to an ultrasonic extrusion apparatus which has an increased number of ultrasonic vibrators provided around the extrusion die in a circumferential direction to increase the vibration output, whereby when extruding a metal material such as a magnesium material, friction between the metal material and the extrusion die can be reduced, thus improving the performance of the extrusion process (preventing a reduction in an extrusion rate, generation of heat, cracking of a product, errors in measurements, etc.).
2. Description of the Related Art
Generally, it is difficult to shape a metal material such as a magnesium material because of friction between tools and the material to be shaped.
For this reason, an extrusion method is mainly used to shape a metal material. Typically, as shown in FIG. 1A, the method of extruding a metal material includes passing a molten metal material 20 through an extrusion die 10, thus forming a metal product 22 having a desired shape.
This metal extrusion method is a method which is used to manufacture high-density and high-quality products at a high production rate. However, the conventional extrusion method has many problems which occur because of friction between the extrusion die 10 and the metal material 20 to be extruded.
To overcome these problems, as shown in FIG. 1B, a technique was proposed, in which an ultrasonic vibrator 10 applies ultrasonic resonance to the extrusion die 10 which shapes a metal material, thus minimizing friction between the extrusion die 10 and the metal material, thereby enhancing the effectiveness of the extrusion process.
FIG. 2 shoos a conventional ultrasonic resonance system 50 in which ultrasonic resonance is applied to the extrusion die 10 to reduce friction between an extrusion material 20 and an extrusion die 10, thus improving the process of forming a rod-shaped product.
In the conventional ultrasonic resonance system 50, two ultrasonic vibrators 40 are respectively provided on upper and lower portions of too extrusion die 10. The ultrasonic vibrators 40 generate ultrasonic waves. For this, an ultrasonic wave generator 60, first and second amplifiers 62 and 64, a pressure controller 66, an oscilloscope 68, a heater controller 70, etc. are connected to the ultrasonic vibrators 40.
In detail, the ultrasonic wave generator 60 outputs a voltage at 10V in a from of sine wave to operate the ultrasonic vibrators 40. Each of the first and second amplifiers 62 and 64 amplifies the voltage output from the ultrasonic wave generator 60 to from 10 to 100 times and supplies it to the corresponding ultrasonic vibrator 40.
Furthermore, the pressure controller 66 controls a piston 72 of a double-acting extruder with a pressure ranging from 0 ton to 500 tons. The oscilloscope 68 measures the voltage and current applied to the ultrasonic vibrators 40. The heater controller 70 maintains the temperature of extrusion material (magnesium) 20, which is approximately 200° C., so that the extrusion material 20 is prevented from being cooled.
As shown in FIG. 3, compared to the metal extrusion method using no ultrasonic vibrator, the conventional ultrasonic resonance system 50 having the above-mentioned construction can markedly reduce friction between the extrusion die 10 and the extrusion material 20, thus making it possible to manufacture higher-density and higher-quality metal products at a high production rate.
However, as shown in FIG. 4, in the case of the extrusion die 10 provided in the conventional ultrasonic resonance system 50, opposite surfaces of a die body 12 which is fixed between an extruder heater 82 and a die holder 34 are planar. An extrusion hole which has a cylindrical or polygonal shape having a constant cross-sectional area is transversely formed through a central portion of the extrusion die 10
Furthermore, a plurality of mounting holes 16 are formed in a circumferential outer surface of the die body 12 at diametrically opposite positions. The two ultrasonic vibrators 40 are fastened to two portions of the die body 12 through the corresponding amounting holes 16 end apply vibrations to the extrusion die 10.
However, in the conventional extrusion die 10, a front surface of the die body 12 is a planar surface and is brought into direct contact with the extrusion material 20. Thus, extrusion pressure, ranging from about 90 tons to about 150 tons, for extruding the extrusion material 20 is directly transmitted to the front surface of the die body 12. A rear surface of the die body 12 is also planar, is brought into close contact with a front surface of the die holder 84, and is reliably integrally fixed to the die holder 84.
Therefore, in the case of the conventional extrusion die 10, even if vibrations are applied from the ultrasonic vibrators 40 to the extrusion die 10, they are disturbed by high extrusion pressure of the extrusion material 20 and dispersed to the outside through the die holder 84. Thus, the vibrations cannot be effectively transmitted to the extrusion die 10, so it is difficult to obtain a satisfactory vibration effect. Moreover, a phenomenon in which a vibration mode deviates from normal conditions is also caused.
In addition, because only the two ultrasonic vibrators 40 that are disposed on the upper and lower portions of the die body 12 apply vibrations to the die body 12 in the directions facing each other, vibrations cannot be evenly applied to the overall shaping space in the extrusion die 10, but vibrations are partially applied to only the upper and lower portions of the die body 12, thus greatly reducing substantial ultrasonic vibration effect.